1. Outburst of EX Lupi
ATel 15271 reports that the type star of the EXOR class, EX Lupi, is going into a major outburst, getting brighter by about 0.064 mag/day. These events are interpreted as increases in the accretion rate from the circumstellar disk onto the star. Outbursts of EX Lup in 1955 and 2008 reached 5 mag above quiescence and lasted for about half a year, and a few sporadic, smaller bursts of EX Lup in the 1990s peaked at about the current brightness and were much shorter than the 1955 and 2008 bursts. The ASAS-SN lightcurve of EX Lup was stable in 2018-2019 with an average brightness of g=13.54 in 2018-2019, had some small bursts of ~0.8 mag in 2020, and then was stable at g=13.34 in 2021.
We now have a unique opportunity to study the rise of an EX Lup outburst. Such studies were not possible for the 2008 outburst because the rise occurred when EX Lup was behind the sun. If this burst reaches 5 mag above the quiescent level, we should have 1-2 more months to follow the changes in the system during the rise. We encourage spectroscopic and photometric monitoring across the electromagnetic spectrum to understand the causes and consequences of what will likely be the 2022 outburst of EX Lup.
AAVSO Participation
Dr. Christian Knigge of Southampton University, who has requested AAVSO data, says "These outbursts might be due to the same disk instability that is responsible for dwarf nova eruptions, but nobody knows for sure. One way to test this would be by observing the colour evolution all the way around the outburst. This has apparently never been done properly - usually all of these sorts of outbursts are only covered once near peak. The outbursts last a long time - quite possibly a year or so (so of course there are seasonal gaps). But the nice thing is that if we could just get multi-colour snapshots on a ~daily basis, starting right now, that would be immensely valuable. It's a very bright object - around 8-12 mags, depending on state, so it's 'easy'."
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2. V1117 Her: Crazy Activity!The highly-atypical YSO (probably a debris-disc object like RZ Psc) V1117 Herculis, has started to behave in a highly peculiar manner. On March 10 I received a note from our member John Pickett that this star had faded to a minimum of 15.1. This in itself was strange as only two months before Peter Bealo told me of another fall to the same magnitude! For years it seems the star had undergone these deep fades, separated by about 13 months - and here we had two such fades in three months! AAVSO colleague and friend Gary Poyner later confirmed on the 12th the star was rising back, at about 13th mag - but just over a week later saw it fade again!
So, from being a star showing these UXOR-like fades every 400 days, its 'period' is now two weeks! It is quite likely that by the time you are reading this, V1117 Her could be doing something similar. What is going on there is anyone's guess. If it is indeed a UXOR then this activity could be seen possibly as the influence of a separate, closer-in planetesimal - but surely such processes take many years, not a fortnight!
Maria Kun's 2014 paper on this object gave a probable distance of 860pc based on its absolute magnitude of 2.4. However thanks to Gaia, we now have an accurate figure, which is much higher - 1416 parsecs! That will mean several assumptions about the star will have to be changed - for instance, that paper gave a distance from the galactic plane of 430pc but this new data produces an even greater distance of 788 parsecs, which decreases even further the likelihood of a 'standard' YSO. Based on these figures from Gaia gives a rough proper motion (rough because as the star is quite close to the celestial equator I ignored the cos2δ element in the calculation) of 8.9 mas/yr. Indeed the paper closes by saying "...reliable measurements of parallax, proper motion, and radial velocity, expected from Gaia, will certainly solve the contradictions in the observed properties of this star" |
